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Modeling
GEYSER
Eruptions in the
by Stephen Mattox
and Christine Webster
Classroom
W
atching Old Faithful transform from a smoldering mound to an explosive
50-meter high geyser is enough to generate awe in any observer. Behind this
stunning, visual geologic display is a triad of heat, water, and plumbing that
rarely unify on our planet. But geologists aren’t the only scientists drawn to
geysers. Biologists have recently recognized thermal features as a habitat of interesting bacteria that thrive in extreme conditions and may provide clues to the origin of life. Engineers
tap into the steam and hot water found in thermal areas around the Pacific Rim to generate
electricity without releasing the carbon dioxide associated with fossil fuels.
Geysers provide an excellent opportunity to explore the Earth system as described by
the National Science Education Standards (content standard D for grades 5–8). By using
the geyser model activity described in this article, students can investigate the relationship
between the hydrosphere, geosphere, and biosphere. In addition, students will be able to
develop descriptions, explanations, and predictions using the model as a guide for their
exploration and apply their thinking to their local setting.
How geysers work
During an eruption cycle, groundwater flows laterally to recharge a shallow plumbing
system (Figure 1). The water is heated by the surrounding hot rock. Pressure (and boiling
temperature) varies in the system depending on the depth of water. As hot water turns to
steam, bubbles form and grow on the walls of the chamber. Large bubbles collect in narrow
passages and generate higher pressure. Eventually gas pressure drives water out at the surface. Once water belches onto the surface, pressure in the entire system is released. Superheated water expands into the areas formerly occupied by the water and converts to steam
as pressure drops in the system, ejecting a fountain of water and steam. When the gas
pressure below is relieved, the eruption ends. The eruption cycle continues as groundwater
flows laterally to recharge the system, heat is added, and pressure builds.
Safety first
Safety is paramount because the model involves boiling water. Wraparound safety
glasses are required for all students. The model should be assembled on a lab table
that students can gather around, but they should be kept at least three meters from
Stephen Mattox is an assistant professor of geology at Grand Valley State University in Allendale, Michigan.
Christine Webster is a science teacher at Hudsonville High School in Hudsonville, Michigan.
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the model during the eruption cycle. Boiling water commonly erupts about 1 to 2 meters above the titration tube.
In addition to safety glasses, the demonstrator should wear
insulated gloves and a lab apron. Start the eruption by simply turning the hot plate on. If needed, the hot plate can
be turned off by unplugging it at the wall.
The discussion before the eruption
To engage students, ask those who have seen a geyser in
person to describe its behavior, appearance, surrounding
geology, and location. Next, distribute the student activity
sheet with questions (page 45), which will lead students
through the activity. The first step of the activity is for
students to sketch the model setup. They then make observations, which will center around the formation of bubbles
within the system. Bubbles begin to form in only a few
minutes. Students will need to be about one meter from
the flask to see the bubbles. If the bubbles are difficult to
see, add a backdrop of colored paper or a few drops of dye
to the water. Students should also explain how the model
compares to real geysers. Specifically, they need to explain
that a source of energy is needed to convert the liquid to a
gas in both systems. The energy is provided by hot rock and
magma in a geyser and by the hot plate in the model.
Students continue to make observations through several eruption cycles. During a typical run, the model can
erupt 20 to 25 times in a five-minute period. Stopwatches
can be used to time the length of each cycle. An eruption
cycle is defined as the time from one eruption to the next.
An eruption occurs when water is forced out of the tube.
Eruptions will continue as long as water is available, heat
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is supplied, and the “plumbing” remains intact (no leaks
or breaks). When the volume of water is low, the eruptions tend to be larger because the ratio of gas to water has
increased. Guide the students toward this observation with
questions such as, What is changing in the system?, Why
is it changing?, and Does this happen in real geysers? After
observing a few cycles, students return to their desks to
complete their activity sheets.
Classroom discussion
The following is a summary of what to look for when assessing students’ responses on the activity sheet. If time
permits, the responses can be shared and discussed with the
class as a whole. Responses to questions 6 through 13 provide an assessment of student understanding. See answers
below (in italic).
1. Make a drawing of the setup in front of you. Label as
much as you can.
Compare to Figure 2. The drawing should include the heat
source, plumbing, and water.
2. As the water begins to boil, record in detail what is happening. (Hint: Look for bubbles.)
As evaporation occurs, small bubbles form on the bottom
of the flask. The bubbles rise up
towards the top of the flask. This is
the onset of the process. The bubbles
are not yet leaving. They are in the
flask. The bubbles are accumulating, Explore geysers at
growing, coalescing, but the system is www.scilinks.org.
Enter code SS040501
open at the top of the titration tube.
Building the geyser
Materials
• a 50-mL titration tube
• a 500-mL Erlenmeyer flask
• a solid rubber stopper (#7)
that will fit the mouth of the flask
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ring stand
a hot plate
three or four stopwatches
burette clamp (metal)
• water
• safety glasses
Procedure
1. Use a power drill with a steel bit to drill a hole in the rubber stopper just big enough so that the titration tube can be snugly
inserted. Alternatively, order a one-hole rubber stopper. The seal between the stopper and tube should be tight.
2. Slide the tubing far enough into the stopper so that, when the stopper is inserted into the flask, the tubing will reach 1–2
cm above the bottom of the flask.
3. Fill the flask with 150–200 mL of water.
4. Place the flask on the hot plate.
5. Insert the stopper-tubing setup into the neck of the flask.
6. Secure the upper end of the tubing to the ring stand with the burette clamp. See Figure 2 for a picture of the
completed setup.
Note: Experiment ahead of time with the temperature settings on the hot plate to find a temperature that will bring the water to a
boil five to ten minutes after it is turned on. You will use this time for a discussion of the processes involved.
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FIGURE 1
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A subsurface model for Old
Faithful in eruption
3. What are the bubbles doing to the level of the water?
The expansion of bubbles as they rise up the tube is forcing
the water up the titration tube. The steam and the expanding
heated air trapped in the system create the pressure.
4. How long does it take for water to rise, erupt, and
then lower?
Times vary from about 10 to 25 seconds.
5. Time three more eruptions and record their durations.
Times vary from about 10 to 25 seconds.
6. Based upon what you have observed, list three factors
that are needed to make an eruption.
Heat, narrowness of tube, and water.
7. How is water heated close to the Earth’s surface?
By hot rock or magma.
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FIGURE 2
Geyser activity setup
18. What is the supply of water for a geyser?
Groundwater that is recharged by surface water.
19. Using the list from question 6, what would be the
greatest determining factor as to how high the eruption would go into the air? Explain your answer.
Answers will vary but key aspects are intensity of heat,
amount of gas pressure, and diameter of the tube.
10. In the eruption cycle data, were the times similar? Explain why or why not.
In general, yes. Once the system began to erupt, it quickly
ejected most of the water and steam. It took a bit longer to
get the last bits of water and steam out.
11. Why did the eruption stop? Give two explanations.
Most of the water was ejected or there was too little gas to
eject what water was left.
12. Compare and contrast Figure 1 with the model drawing you
made in question 1. Write your answers in the table below.
See completed table below.
13. Based on your observations, explain the presence or
absence of geysers in
• Yellowstone (hot rock, shallow groundwater, good
plumbing all present)
• Hawaii (groundwater is too deep)
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Michigan (midwestern states, no heat source)
Your home state (varies)
Answer to question 12: Comparison of the model geyser
to real geysers
Model
Geyser
Heat source Hot plate
Magma or hot
rock
Water
Small volume of water
from the tap
Larger volume
of water that
is replaced by
surface runoff
and supplied by
groundwater
Plumbing
Plumbing is a straight
glass tube
Plumbing is
complex with
narrow curved
tunnels
Pressure
Weight of water column
Weight of water
column
System
Closed to water recharge Open system
but open to atmosphere
Erupted
material
Steam and/or water
Steam and/or
water
Eruption
cycle
Tens of seconds
Constant to
years
Eruption
size
Eruption is several
centimeters up into the
air over an area of about
100 square cm
Eruption can be
up to hundreds
of meters high
over an area
of hundreds of
square meters
Geographic Classrooms everywhere!
distribution
Ring of Fire,
some hot spots
Host for
thermophiles
Some
None
Extension questions
• How could the model be modified to generate electricity? Would this system be energy efficient? Would it be
comparable to geothermal power plants?
• Repeat the activity and vary the following: The volume
of the flask, the shape of the flask, the height of the water column, and/or the diameter of the glass column.
• Suggest how the model could be modified to erupt every
hour, to erupt larger volumes, or to erupt higher into the air.
• Compare the new eruptions to real geysers.
Reference
Keefer, W. R. 1972. The geologic story of Yellowstone National
Park. U.S. Geological Survey Bulletin 1347: 92.
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Student activity sheet
1.
Make a drawing of the setup in front of you. Label as
much as you can.
2. As the water begins to boil, record in detail what is
happening. (Hint: Look for bubbles.)
3. What are the bubbles doing to the level of the water?
4. How long does it take for the water to rise up the tube,
erupt, and then drop back down? This is an eruption
cycle. Begin timing the cycles after the first eruption.
5. Time three more eruptions and record their
durations.
6. Based upon what you have observed, list three factors
that are needed to make an eruption occur.
7. How is water heated close to the Earth’s surface?
8. What is the supply of water for a geyser?
9. Using the list from question 6, what would be the
greatest determining factor as to how high the eruption
would go into the air? What would you modify to
make a shorter/higher/longer eruption? Explain your
answer.
10. In the eruption cycle data, were the times similar?
Explain why or why not.
11. Why did the eruption stop? Give two explanations.
12. Compare and contrast Figure 1 with the model drawing
you made in question 1. Write your answers in the data
table below.
13. Based on your observations, explain the presence or
absence of geysers in
• Yellowstone,
• Hawaii,
• Michigan (midwestern states), and
• Your home state.
Comparison of the model geyser to real geysers
Model
Geyser
Heat source
Water
Plumbing
Pressure
System
Erupted
material
Eruption cycle
Eruption size
Geographic
distribution
Host for
thermophiles
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